For Aaron Chu's birthday he gets a baseball card of his favorite player Rusty McClure. A card from McClure second year. But his friends, The Number Investigators, discover that he really wants a McClure rookie card. Marcus and the other number investigators make a deal with Aaron that he can make enough money to buy a McClure rookie card. The problem is, a nice rookie card is expensive. So the Number Investigators decide to help Aaron out by organizing a lemonade stand and baseball card show. Aaron will try and sell of his other cards in order to earn enough to purchase a McClure rookie card. Even if he sells some of his cards, will it be enough?